Maximum sustainable yield (MSY) is applied as a global management principle for marine fisheries. It reflects a focus on obtaining continuing high catches to provide food and livelihoods to humanity while not compromising ecosystems. However, maintaining stocks to provide the MSY on a single species basis is challenging because achieving MSY for an individual stock can hamper the achievement of MSY for other stocks. This also doesn't ensure that broader ecosystem, economic, and social objectives are addressed.
The article by Rindorf et al investigates how the principles of MSY, expanded through a 'pretty good yield' range of fishing mortalities providing more than 95% of the average single stock yield, can be further developed to a Pretty Good Multispecies Yield (PGMY) space. It can also be developed further to a pretty good multidimensional yield to accommodate situations where the yield from a stock affects the ecosystem, economic and social benefits, or sustainability.
The study demonstrates, through a European example, that PGMY is a practical concept. As PGMY provides a safe operating space for management that adheres to the principles of MSY, it allows the consideration of other aspects to be included in operational management advice in both data-rich and data-limited situations. PGMY also provides a way to integrate advice across stocks, avoiding clearly infeasible management combinations and thereby hopefully increasing confidence in scientific advice.
Scientific advice on annual catch based on PGMY principles for mixed fisheries could have four steps: 1) Determining the single species ranges, 2) determining which combinations of fishing mortalities for different species are compatible with multispecies and ecosystem considerations, 3) determining which combinations are desirable from an economic perspective, and 4) determining which combinations are desirable from a social perspective.
The study provides a demonstration of the first two steps for cod and haddock in the North Sea. Due to the cannibalistic nature of cod, low values of cod fishing mortality lead to yields of the fish below 95% of MSY as well as increased risk of prey stocks falling below biomass reference points. On the other hand, technical interactions in the fisheries mean that it is not possible to retain a high fishing mortality on haddock with a low fishing mortality on cod.
The insights and results from this study provide a possible way forward in the practical implementation of an ecosystem approach to fisheries management which satisfies the ecological, economic, social, and governance pillars of sustainability.